The rules of setting leap in the lunar calendar are related to solar terms. 24 solar terms can be divided into two categories: solar terms and neutral gas, referred to as "solar terms and harmony". From the winter solstice, the ancients alternately arranged the middle qi and solar terms, so slight cold is the solar term, great cold is the middle qi, and so on. There are 12 solar terms and 12 solar terms in a year. Generally, there is a solar term and a solar term every month. Every gas belongs to a certain month and cannot be confused.

According to the records of the Song Dynasty, Wen Yanbo put down the Wangze Uprising in Zhou Bei in the first month of A.D. 1048.

The first leap month is a rare leap month, which did not appear in18th century, 20th ~ 2nd1century, 25th century and 28th ~ 4th1century. The last leap month appeared in 17 century 165 1 year (xinmao year), and the next leap month will appear in 22 century148 year (Wushen year).

The year of leap January must be the earliest year of Spring Festival.

The rotation of the earth brings us the first natural time unit "day", the revolution of the earth around the sun brings us the second time unit "year", and the revolution of the moon around the earth establishes the third time unit "month".